Fluidized bed furnace and waste treatment method

ABSTRACT

A waste treatment technique includes: blowing a fluidizing gas from around a non-combustible substance discharge port toward fluidizable particles to form a first fluidization region, while blowing a fluidizing gas between the first fluidization region and a front wall at a flow velocity less than that in the first fluidization region to form a second fluid region having a relatively low degree of fluidization of fluidizable particles; returning fluidizable particles discharged from the non-combustible substance discharge port to a fluidized bed from the side of the front wall to form, in the fluidized bed, a flow of fluidizable particles directed from the front wall to the non-combustible substance discharge port; supplying waste from the front wall onto the fluidized bed to cause the waste to be accumulated on the second fluidization region while causing the accumulated waste to be moved into the first fluidization region step-by-step and gasified.

TECHNICAL FIELD

The present invention relates to a fluidized bed furnace designed to heat waste in a fluidized bed formed by fluidizing fluidizable particles to thereby extract a combustible gas from the waste, and a waste treatment method.

BACKGROUND ART

Heretofore, as a fluidized bed furnace, there has been known one type described in the following Patent Document 1. As illustrated in FIG. 11, this fluidized bed furnace comprises a furnace body 104 having fluidizable sand (fluidizable particles) 102 in a furnace bottom section, and an air supply section 106 for supplying air into the fluidizable sand 102 in the furnace bottom section so as to fluidize the fluidizable sand 102 to form a fluidized bed. The furnace body 104 has a sidewall. The sidewall is provided with an input section 108 for inputting waste onto the fluidized bed therefrom.

In this fluidized bed furnace 100, the air supply section 106 is adapted to supply air into high-temperature fluidizable sand 102. Consequently, the fluidizable sand 102 is fluidized in a levitated or suspended state to form a fluidized bed. In this process, the air supply section 106 is adapted to supply air in such a manner that a fluidized state of the fluidizable sand 102 becomes approximately equalized in the entire region of the fluidized bed so as to allow waste input from the input section 108 onto the fluidized bed to be entrapped inside the fluidized bed and efficiently combusted.

Every time waste is input from the input section 108 onto the high-temperature fluidizable sand 102, the input waste is mixed with the high-temperature fluidizable sand 102 of the fluidized bed, and thermally decomposed (gasified). Consequently, a combustible gas is generated. For example, this combustible gas will be combusted at high temperatures in a melting furnace in a subsequent stage.

Waste input into the fluidized bed furnace 100 is entrapped in the active fluidized bed and combusted or gasified. In this process, every time waste is intermittently input, combustible substances in the waste are rapidly combusted, so that a rapid fluctuation in amount, concentration, etc., of a generated combustible gas will repeatedly occur. A change in the gasification reaction is largely dependent on a quantitative characteristic in supply of waste. Thus, in the case where there is a fluctuation in supply of waste or a qualitative change in components of waste, it is impossible to stably generate a combustible gas. Particularly, when a large amount of easily combustible trash such as paper or sheet-shaped plastic is comprised in waste, a fluctuation of generation of a combustible gas becomes larger, and therefore there is a need for stabilizing the gas generation.

For example, in the case where generated combustible gas is used for a gas engine to generate electric power, if a combustible gas is generated with large fluctuations, it is impossible to obtain stable energy. Therefore, there is a need for further stabilizing a combustible gas to be obtained in a fluidized bed furnace.

LIST OF PRIOR ART DOCUMENTS

Patent Documents

-   Patent Document 1: JP 2006-242454A

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fluidized bed furnace capable of stably obtaining a combustible gas even from waste comprising easily combustible trash, and a waste treatment method.

According to one aspect of the present invention, there is provided a fluidized bed furnace for heating waste to extract a combustible gas from the waste. The fluidized bed furnace comprises: fluidizable particles making up a fluidized bed to heat the waste; a furnace body having a bottom wall supporting the fluidizable particles from therebelow, and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a non-combustible substance discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance discharge port; a gas supply section for blowing a fluidizing gas from the bottom wall of the furnace body toward the fluidizable particles to fluidize the fluidizable particles; a waste supply section for supplying waste from a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste on the fluidized bed to be moved toward the non-combustible substance discharge port; and a sand circulation device for returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the waste supply section to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion located on the side opposite to the non-combustible substance discharge port, to the non-combustible substance discharge port. The gas supply section is adapted to blow the fluidizing gas from around the non-combustible substance discharge port to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern and mixed with the waste to gasify the waste, while blowing the fluidizing gas between the first fluidization region and the waste supply section at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles lower than that in the first fluidization region, and the waste supply section is adapted to supply waste from the supply-side sidewall portion to the fluidized bed to cause the waste to be accumulated on the second fluidization region while causing the accumulated waste to be moved into the first fluidization region step-by-step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a fluidized bed furnace according to one embodiment of the present invention.

FIG. 2 is a horizontal sectional view of a furnace body, for explaining an introduction position of waste and an introduction position of fluidizable particles in the fluidized bed furnace.

FIG. 3 is a diagram for explaining a nozzle arrangement in a bottom wall of the furnace body.

FIG. 4 is a diagram for explaining a configuration for pushing fluidizable particles directly onto a fluidized bed in the furnace body.

FIG. 5 is a diagram for explaining a furnace body having a reflecting portion in a front wall thereof, in a fluidized bed furnace according to another embodiment of the present invention.

FIG. 6 is a diagram for explaining a furnace body having a guide portion in a rear wall thereof, in a fluidized bed furnace according to yet another embodiment of the present invention.

FIG. 7 is a diagram for explaining a furnace body having a roof portion in each of front and rear walls thereof, in a fluidized bed furnace according to still another embodiment of the present invention.

FIG. 8 is a diagram for explaining a furnace body having a bent bottom wall thereof, in a fluidized bed furnace according to yet still another embodiment of the present invention.

FIG. 9 is a diagram for explaining a furnace body comprising a thermometer and an air supply section, in a fluidized bed furnace according to another further embodiment of the present invention.

FIG. 10 is a diagram for explaining a waste supply section, in a fluidized bed furnace according to still a further embodiment of the present invention.

FIG. 11 is a schematic configuration diagram of a conventional fluidized bed furnace.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, the present invention will now be described based on one embodiment thereof.

A fluidized bed furnace according to this embodiment is designed to heat waste by high-temperature fluidizable particles, to extract a combustible gas from the waste. As illustrated in FIG. 1, the fluidized bed furnace comprises fluidizable particles 12, a furnace body 20, a gas supply section 30, a waste supply section 40 and a sand circulation device 50.

The fluidizable particles 12 are particles make up a fluidized bed 14 to heat waste 18, inside the furnace body 20. More specifically, the fluidizable particles 12 are mixed with waste 18 while being heated up to a high temperature by combustion of a part of waste components, so that the waste 18 is gasified to generate a combustible gas. For example, the fluidizable particles 12 may be silica sand.

The furnace body 20 is configured to internally have the fluidizable particles 12 and extract a combustible gas from waste 18 by means of the fluidizable particles 12 in a high temperature state. The furnace body 20 has a bottom wall 21 supporting the fluidizable particles 12 from therebelow, a sidewall 22 standing upwardly from the bottom wall 21, and a combustible gas outlet portion 23 provided at an upper end of the sidewall 22.

The sidewall 22 has a rectangular tubular shape extending in an up-down (vertical) direction. Specifically, as also illustrated in FIG. 2, the sidewall 22 has a front wall (supply-side sidewall portion) 24 and a rear wall 25 which are disposed in opposed and spaced-apart relation to each other in a front-rear direction (in FIG. 2, in a right-left direction), and a pair of lateral walls 26, 26 each connecting corresponding ends of the front wall 24 and the rear wall 25. The lateral walls 26, 26 are disposed parallel to each other. In other words, the furnace body 20 has a shape in plan view, in which a dimension in a width direction (widthwise dimension) as a distance between the lateral walls 26, 26 is equalized in the front-rear direction.

A portion (front wall) 24 of the sidewall 22 located on a side opposite to an aftermentioned non-combustible substance discharge port 29 across a center position of the bottom wall 21 has a sand introduction section 27 and a waste introduction port 28. The sand introduction section 27 is adapted to introduce fluidizable particles 12 into the furnace body 20, and the waste introduction port 28 is adapted to introduce waste 18 into the furnace body 20.

Specifically, the sand introduction section 27 is provided at each of widthwise opposite ends of a lower portion of the front wall 24 to allow fluidizable particles to be introduced to widthwise opposite end areas of an inside of the furnace body 20 (see FIG. 2). The sand introduction section 27 is provided at a height position where fluidizable particles 12 can be input from above the fluidizable particles 12 supported by the bottom wall 21 (fluidized bed 14), toward the fluidized bed 14. It is to be noted that an input area of fluidizable particles 12 is not limited to the widthwise opposite end areas. For example, the input area of fluidizable particles 12 may be one of the widthwise opposite end areas. Alternatively, the input area of fluidizable particles 12 may be an upper surface of the introduced waste 18 (a central area adjacent to the front wall 24 in FIG. 2). In the case where fluidizable particles 12 are input onto waste 18, the fluidizable particles 12 serve as an ignition source to allow only easily combustible trash to be stably combusted (gasified) initially.

The waste introduction port 28 is provided in approximately the entire region of the lower portion of the front wall 24 in the width direction. The waste introduction port 28 is provided at a height position where waste 18 can be pushed generally horizontally onto an upper surface of the fluidized bed 14 made up of the fluidizable particles 12 supported by the bottom end 21. In other words, the waste introduction port 28 is provided in such a manner that a lower end thereof is located at a position slightly higher than the upper surface of the fluidized bed 14.

The combustible gas outlet portion 23 is designed to discharge a combustible gas generated inside the furnace body 20. The combustible gas outlet portion 23 has an outer diameter squeezed more than the sidewall 22, so that a duct or the like for supplying the combustible gas obtained in the furnace body 20 to a subsequent stage, for example, a gas engine for electric power generation processes, can be connected thereto.

The bottom wall 21 has a non-combustible substance discharge port 29 provided at a position offset from the center position thereof in a specific direction to discharge non-combustible substances in waste 18 together with a part of the fluidizable particles 12. The non-combustible substance discharge port 29 has an opening extending over the widthwise entire region of the bottom wall 21. The bottom wall 21 has an upper surface 21 a is inclined to become lower toward the non-combustible substance discharge port 29 so as to cause the non-combustible substances to fall on the upper surface 21 a. The bottom wall 21 in this embodiment has a non-combustible substance discharge port 29 at a position offset rearwardly, and an upper surface 21 a of the bottom wall 21 extends rearwardly (in FIG. 1, in a left-to-right direction) at a constant downward inclination. Specifically, the upper surface 21 a of the bottom wall 21 has an inclination angle of 15 degrees to 25 degrees with respect to a horizontal plane.

The gas supply section 30 is designed to blow a fluidizing gas from the bottom wall 21 toward the fluidizable particles 12 to fluidize the fluidizable particles 12. The gas supply section 30 comprises a plurality of nozzles 31 for blowing the fluidizing gas, a gas box 32 for supplying the fluidizing gas to the nozzles 31, and a gas feeding unit 33 for feeding the fluidizing gas to the gas box 32.

The plurality of nozzles 31 are installed to the bottom wall 21 in spaced-apart relation to each other in the width direction and the front-rear direction, i.e., in a lattice arrangement. Each of the nozzles 31 is attached to the bottom wall 21 to penetrate through the bottom wall 21. In this embodiment, as also illustrated in FIG. 3, the bottom wall 21 is divided into a front region 21 b and a rear region 21 c. Then, the plurality of nozzles 31 are installed to the front and rear regions 21 b, 21 c in such a manner that the number of nozzles 31 provided in the front region 21 b becomes greater than the number of nozzles 31 provided in the rear region 21 c. It is to be noted that a relationship between the respective numbers of nozzles 31 in the front and rear regions 21 b, 21 c is not particularly limited. For example, the number of nozzles 31 in the front region 21 b may be equal to the number of nozzles 31 in the rear region 21 c. Alternatively, the number of nozzles 31 in the rear region 21 c may be greater than the number of nozzles 31 in the front region 21 b.

The gas box 32 has a box shape extending in the width direction. The gas box 32 serves as a header for distributing the fluidizing gas to an array of the nozzles 31 arranged side-by-side in the width direction in the bottom wall 21. The gas box 32 has a function of equalizing respective flow volumes of the fluidizing gas to be blown from the array of nozzles 31 arranged in the width direction. In this embodiment, a plurality of the gas boxes 32 are provided on the side of a lower surface of the bottom wall 21 and arranged side-by-side in the front-rear direction. Thus, with respect to each of a plurality of the arrays of nozzles 31 corresponding to respective ones of the gas boxes 32, the flow volume of the fluidizing gas to be blown from the array of nozzles 31 can be changed. In this embodiment, five gas boxes 32 a, 32 b, 32 c, 32 d, 32 e are arranged side-by-side in the front-rear direction. Specifically, four gas boxes 32 a, 32 b, 32 c, 32 d are disposed on the side of the front wall 24 with respect to the non-combustible substance discharge port 29, and one gas box 32 e is disposed on the side of the rear wall 25 with respect to the non-combustible substance discharge port 29.

The gas feeding unit 33 is designed to feed (supply) the fluidizing gas to the respective gas boxes 32. The gas feeding unit 33 is capable of feeding the fluidizing gas to each of the gas boxes 32 in a different flow volume. The gas feeding unit 33 in this embodiment is configured to feed the fluidizing gas to two of the gas boxes 32 adjacent to each other in the front-rear direction, in such a manner that a flow volume of the fluidizing gas to be fed to a rear one of the adjacent gas boxes 32 becomes greater than a flow volume of the fluidizing gas to be fed to a front one of the adjacent gas boxes 32. The gas feeding unit 33 is adapted to feed only air to the respective gas boxes 32 to serve as the fluidizing gas. Alternatively, an inert gas such as nitrogen may be fed in combination with the air.

Specifically, during a normal operation of the fluidized bed furnace 10, i.e., when waste 18 is introduced into the furnace body 20 to generate a combustible gas from the introduced waste 18, the gas feeding unit 33 is operable to cause the fluidizing gas to be blown from around the non-combustible substance discharge port 29. In this process, the gas feeding unit 33 is operable to form a first fluidization region 15 where the fluidizable particles 12 are moved in a convection-like pattern and mixed with the introduced waste 18 to gasify the waste 18. Concurrently, the gas feeding unit 33 is operable to blow the fluidizing gas between the first fluidization region 15 and the front wall 24 at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region 15, to form a second fluidization region 16 having a degree of fluidization of the fluidizable particles 12 lower than that in the first fluidization region 15. More specifically, as mentioned above, the gas feeding unit 33 is configured such that a flow volume of the fluidizing gas to be fed to a rear one (e.g., the gas box 32 c) of the gas boxes 32 adjacent to each other in the front-rear direction becomes greater than a flow volume of the fluidizing gas to be fed to a front one (e.g., the gas box 32 b) of the adjacent gas boxes 32. In this case, the gas feeding unit 33 is operable to, in the fluidized bed 14, form a first fluidization region 15 actively fluidized, around the non-combustible substance discharge port 29, while forming a second fluidization region 16 restrained in fluidization, between the first fluidization region 15 and the front wall 24. Alternatively, the gas feeding unit 33 may be configured such that a flow volume of the fluidizing gas to be fed to each of the gas boxes 32 c, 32 d, 32 e on the side of the rear wall 25 becomes greater than a flow volume of the fluidizing gas to be fed to each of the gas boxes 32 a, 32 b on the side of the front wall 24. In this case, the gas feeding unit 33 is operable to, in the fluidized bed 14, form a second fluidization region 16 restrained in fluidization, in a region corresponding to the gas boxes 32 a, 32 b on the side of the front wall 24, while forming a first fluidization region 15 actively fluidized, in a region corresponding to the gas boxes 32 c, 32 d, 32 e on the side of the rear wall 25.

Specifically, the gas feeding unit 33 is adapted to cause the fluidizing gas to be blown in the second fluidization region 16 at the flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2, and blown in the first fluidization region 15 at the flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5. In this formula, U_(mf) is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles 12. Further, U_(o) is a cross-sectional average flow velocity of the fluidizing gas.

On the other hand, during stop of the fluidized bed furnace 10, i.e., when the introduction of waste 18 into the furnace body 20 is stopped, the gas feeding unit 33 is operable to feed a mixture formed by mixing an inert gas with air, as the fluidizing gas to be supplied to the respective gas boxes 32. Then, the gas feeding unit 33 is operable to gradually increase the inert gas in a ratio between air and the inert gas in the fluidizing gas. Consequently, the gas feeding unit 33 can suppress violent or rapid combustion of the waste 18 remaining in the furnace body 20, thereby restraining a rise in internal temperature of the furnace body 20.

More specifically, during the normal operation, in the furnace body 20, combustion, gasification, etc., of the waste 18 are performed under a condition that an oxygen concentration is set to a value less than that suitable for combustion of the waste 18. In this state, when the introduction of waste 18 into the furnace body 20 is stopped, an amount of combustible substances in the furnace body 20 will be reduced. In this process, the fluidizing gas (air) is continuously supplied into the furnace body 20 in a predetermined flow volume to maintain the fluidized bed 14, so that the oxygen concentration in the furnace body 20 will be increased. When the oxygen concentration in the furnace body 20 reaches a value suitable for combustion of the waste 18 remaining in the furnace body 20, the waste 18 is violently or rapidly combusted, so that the internal temperature of the furnace body 20 becomes higher than that during the normal operation. In such a high-temperature state of the inside of the furnace body 20, the fluidizable particles 12 forming the fluidized bed 14 are agglomerated due to the heat. Once the fluidizable particles 12 are agglomerated, even if the fluidizing gas is subsequently blown into the agglomerated fluidizable particles 12 in order to form the fluidized bed 14, the agglomerated fluidizable particles 12 will never be fluidized. Therefore, the gas feeding unit 33 is operable, when the introduction of waste 18 into the furnace body 20 is stopped, to mix an inert gas with air to be blown into the furnace body 20, and gradually increase the ratio of the inert gas. This allows the oxygen concentration in the furnace body 20 to be kept at a value less than that suitable for combustion of the waste 18. Consequently, it becomes possible to suppress violent or rapid combustion of the waste 18 remaining in the furnace body 20.

Further, the gas feeding unit 33 is adapted to be capable of adjusting a temperature of the fluidizing gas to be fed to the gas boxes 32. The gas feeding unit 33 is operable, upon start of the operation of the fluidized bed furnace 10, to blow the fluidizing gas in a high-temperature state from around the non-combustible substance discharge port 29 toward the fluidizable particles 12. In this way, the gas feeding unit 33 is operable to heat the fluidizable particles 12 until the fluidizable particles 12 reach a temperature capable of performing combustion and gasification of the waste 18. In this case, when the fluidizable particles 12 is heated up to a high temperature and combustion of the waste 18 is started, the temperature of the fluidizable particles 12 will be maintained by the combustion. Thus, the gas feeding unit 33 may be configured to lower the temperature of the fluidizing gas to be fed to the gas boxes 32 just after start of the combustion.

The waste supply section 40 is designed to supply waste 18 from the front wall 24 to a region on the fluidized bed 14 adjacent to the front wall 24. The waste supply section 40 in this embodiment is configured to push waste 18 generally horizontally from the front wall 24 (specifically, the waste introduction port 28 of the front wall 24) onto the fluidized bed 14, thereby causing the waste 18 to be moved toward the non-combustible substance discharge port 29. In other words, the waste supply section 40 is adapted to push waste 18 to cause the waste 18 to be accumulated on the second fluidization region 16 while causing the accumulated waste 18 to be moved into the first fluidization region 15 step-by-step. The waste supply section 40 comprises a pusher 41 and a drive unit (illustration is omitted) for driving the pusher 41. The pusher 41 has a pushing surface 42 extending in the width direction. In this embodiment, the pushing surface 42 has a widthwise length equal to a width of the waste introduction port 28 of the front wall 24. Further, the pushing surface 42 has a vertical length which is approximately a half of a height dimension of an opening of the waste introduction port 28. The pusher 41 is installed to be movable in the front-rear direction, at the same height position as that of the waste introduction port 28. The drive unit comprises a driving power source such as a motor or a cylinder, and is adapted to reciprocatingly move the pusher 41 in the front-rear direction by the driving power. It is to be noted that the waste supply section 40 is not limited to a specific configuration. For example, the waste supply section 40 in this embodiment is configured such that the pusher 41 is employed to push waste 18 into the furnace body. However, the waste supply section may be configured such that a screw extruder or the like is employed to push waste 18 into the furnace body. Based on employing the pusher 41 or the screw extruder, it becomes possible to supply trash which is likely to be scattered due to its small bulk specific gravity, such as paper or plastic sheet, into the furnace body 20 while keeping a massive form. This makes it possible to suppress scattering of trash inside the furnace body 20, as compared to a conventional furnace in which trash is input from an upper portion thereof.

The sand circulation device 50 is designed to return the fluidizable particles 12 discharged from the non-combustible substance discharge port 29, to the fluidized bed 14 at a position on the side of the waste supply section 40 to circulate the fluidizable particles 12. When the sand circulation device 50 operates to return the fluidizable particles 12 discharged from the non-combustible substance discharge port 29, to the fluidized bed 14 at a position on the side of the front wall 24, in the above manner, a flow of the fluidizable particles 12 directed from the front wall 24 to the non-combustible substance discharge port 29 is formed inside the fluidized bed 14. In addition, the second fluidization region 16 is maintained at a high temperature to some extent. The sand circulation device 50 comprises a non-combustible substance discharge section 51, a separation section 52, and a conveyance section 53.

The non-combustible substance discharge section 51 is provided just below the non-combustible substance discharge port 29 of the bottom wall 21, and adapted to move a mixture of non-combustible substances and a part of the fluidizable particles 12 dropping from the non-combustible substance discharge port 29, to the separation section 52. The non-combustible substance discharge section 51 in this embodiment is configured to move the mixture dropping from the non-combustible substance discharge port 29, to the separation section 52 by using a screw extruder. The separation section 52 is adapted to separate the fluidizable particles 12 from the mixture sent from the non-combustible substance discharge section 51. The separation section 52 in this embodiment is configured to separate the fluidizable particles 12 from the mixture by using a sieve. The conveyance section 53 is adapted to convey the fluidizable particles 12 separated in the separation section 52, to the sand introduction section 27, and introduce the conveyed fluidizable particles 12 into the furnace body 20 via the sand introduction section 27.

The sand circulation device 50 in this embodiment is configured to return the fluidizable particles 12 discharged from the non-combustible substance discharge port 29, to the fluidized bed 14 by inputting the fluidizable particles 12 from above the fluidized bed 14 toward an upper surface of the fluidized bed 14. However, it is not limited to this configuration. For example, as illustrated in FIG. 4, the fluidizable particles 12 discharged from the non-combustible substance discharge port 29 may be directly returned to an inside of the fluidized bed 14. In the example illustrated in FIG. 4, a sand introduction section (sand introduction opening) 27A is provided in the front wall 24 at an intermediate height position of the fluidized bed 14. A screw extruder 55 is provided at an end of the conveyance section 53 of the sand circulation device 50 on the side of the furnace body 20, and the furnace body-side end of the conveyance section 53 is inserted into the sand introduction section 27. In this manner, the fluidizable particles 12 discharged from the non-combustible substance discharge port 29 may be returned to the fluidized bed 14 in such a manner as to be directly pushed into the fluidized bed 14. In this case, the sand introduction section 27 is not limited to the intermediate height position of the fluidized bed 14, but may be located on a relatively upper or lower side in a height direction of the fluidized bed 14. When the fluidizable particles 12 are pushed into the fluidized bed 14, a movement of the fluidizable particles 12 in a horizontal direction is more forcibly performed, so that it becomes possible to suppress non-combustible substances from being accumulated on a furnace floor.

In the fluidized bed furnace 10 configured as above, a combustible gas is collected from waste 18 in the following manner.

Upon feeding the fluidizing gas from the gas feeding unit 33 to the respective gas boxes 32, the fluidizing gas is blown from the bottom wall 21 into the furnace body 20 toward the fluidizable particles 12, so that the fluidized bed 14 is formed inside the furnace body 20. In this process, the gas feeding unit 33 adjusts a flow volume of the fluidizing gas to be fed to each of the gas boxes 32. Through this adjustment, in the fluidized bed 14, the first fluidization region 15 actively fluidized is formed on the side of the non-combustible substance discharge port 29, and the second fluidization region 16 restrained in fluidization is formed between the first fluidization region 15 and the front wall 24. Further, the gas feeding unit 33 feeds the fluidizing gas in a high-temperature state to a part (e.g., in this embodiment, the gas boxes 32 c, 32 d, 32 e) of the gas boxes 32 corresponding to the first fluidization region 15 to positively heat the fluidizable particles 12 in the first fluidization region 15.

Concurrently, the sand circulation device 50 circulates the fluidizable particles 12 to form a flow of the fluidizable particles 12 in the fluidized bed. Specifically, the non-combustible substance discharge section 51 sends the fluidizable particles 12 dropping from the non-combustible substance discharge port 29 of the furnace body 20, to the separation section 52. Then, the conveyance section 53 conveys the fluidizable particles 12 passing through the separation section 52, to the sand introduction section 27 of the furnace body 20. The conveyed fluidizable particles 12 are returned to the fluidized bed 14 at a position on the side of the front wall 24, via the sand introduction section 27. When the fluidizable particles 12 discharged from the non-combustible substance discharge port 29 located on the side of the rear wall 25 is returned to the fluidized bed 14 at a position on the side of the front wall 24, in the above manner, a flow of the fluidizable particles 12 directed from the front wall 24 to the non-combustible substance discharge port 29 is formed in the fluidized bed 14. In this process, the fluidizable particles 12 in the first fluidization region 15 in a higher-temperature state are partially discharged from the non-combustible substance discharge port 29, and the sand circulation device 50 returns the discharged fluidizable particles 12 to the fluidized bed 14 at a position on the side of the front wall 24. This allows a temperature of the second fluidization region 16 to be maintained at a predetermined value. However, during the period in which the fluidizable particles 12 discharged from the non-combustible substance discharge port 29 are returned to the fluidized bed 14 by the sand circulation device 50, a temperature of the fluidizable particles 12 is lowered. Therefore, the second fluidization region 16 has a temperature less than that of the first fluidization region 15. Preferably, the temperature of the first fluidization region 15 is kept in the range of 600 to 800° C., whereas the temperature of the second fluidization region 16 is kept in the range of about 400 to 600° C.

When the temperatures of the regions 15, 16 in the fluidized bed 14 within the furnace body 20 reach respective predetermined values, the waste supply section 40 starts to push waste 18 into the furnace body 20 via the waste introduction port 28. Specifically, the pusher 41 driven by the drive unit pushes waste 18 generally horizontally toward the rear wall 25. Through this operation, the waste 18 is pushed onto the second fluidization region 16 at a position adjacent to the front wall 24 (see FIG. 2).

The fluidization of the fluidizable particles 12 in the second fluidization region 16 is restrained. Thus, the pushed waste 18 is not positively mixed with the fluidizable particles 12, so that most of the waste 18 is accumulated on the second fluidization region 16, and heavy non-combustible substances therein sink down. Consequently, in the second fluidization region 16, rapid combustion of the waste 18 is suppressed, and easily-gasifiable substances in the waste are gasified by heat radiation within the furnace body 20. In other words, easily gasifiable waste 18 such as plastic or paper is gasified while being moved in a surface layer of the second fluidization region 16. On the other hand, not-easily gasifiable waste such as a wood piece is partially gasified, but a large part thereof reaches the first fluidization region 15 without being gasified. In this manner, the easily gasifiable waste 18 is gasified under a mild condition in the second fluidization region 16 before it reaches the highly fluidized bed (first fluidization region 15). This makes it possible to suppress a fluctuation of generation of a combustible gas. The accumulated waste 18 is combusted by radiation heat within the furnace body 20, as mentioned above. However, although the radiation heat has a temperature of 800 to 900° C. which is greater than that of the fluidizable particles 12 forming the fluidized bed 14, a contact between the waste 18 and air is not satisfactory. Thus, easily combustible trash, such as paper or sheet-shaped plastic, in waste 18, is mainly gasified. In this process, the second fluidization region 16 has a relatively low temperature, and an amount of air (fluidizing gas) to be supplied to the second fluidization region 16 is relatively small, so that even the easily combustible trash will be gradually gasified. Further, the fluidizable particles 12 are gradually discharged through the non-combustible substance discharge port 29, so that, according to the discharge of the fluidizable particles 12 and the fluidization of the fluidizable particles 12 by the fluidizing gas, a part of the accumulated waste 18 is moved or spread step-by-step in a left-to-right direction in FIG. 1. Therefore, even if waste 18 is input in a massive form, and easily combustible papers are comprised therein, it can be expected to promote gasification of the papers based on a phenomenon that the papers are moved toward a surface of the massive waste during the spreading. As above, in the second fluidization region 16, rapid combustion of the waste 18 is suppressed to prevent a rapid increase of combustible gas during introduction of waste 18.

Subsequently, new waste 18 is pushed into the furnace body 20 via the waste introduction port 28 by the pusher 41. Thus, the waste 18 accumulated on the second fluidization region 16 is pushed by the new waste 18, and moved into the first fluidization region 15 step-by-step. The first fluidization region 15 is actively fluidized and heated up to a high temperature by combustion of the waste 18, so that the waste 18 moved from a position on the second fluidization region 16 is mixed with the fluidizable particles 12 and sufficiently gasified. Consequently, a combustible gas is generated. More specifically, in the fluidized bed 14, a fluidized state gradually becomes more active in a direction from the front wall 24 to the non-combustible substance discharge port 29. Thus, when the waste 18 is moved from a position on the second fluidization region 16 adjacent to the front wall 24 to the first fluidization region 15 step-by-step, it will be gradually mixed with the fluidizable particles 12. Further, an amount of blowing air (fluidizing gas) is gradually increased in the direction from the front wall 24 to the non-combustible substance discharge port 29. Thus, when the waste 18 is moved from the second fluidization region 16 to the first fluidization region 15 step-by-step, it will be gradually combusted, causing an increase in temperature of the fluidizable particles 12. In a region of this high-temperature fluidized bed 14 just above the non-combustible substance discharge port 29 and the vicinity thereof, the waste 18 is sufficiently mixed with the fluidizable particles 12. This allows the uncombusted waste 18 remaining after passing through the second fluidization region 16 to be sufficiently gasified in the first fluidization region 15.

On the other hand, the waste 18 newly pushed onto the second fluidization region 16 by the pusher 41 is accumulated on the second fluidization region 16 almost without being mixed with the fluidizable particles 12 as mentioned above. Then, the accumulated waste 18 is gradually combusted under the condition that violent or rapid combustion is suppressed.

As above, under the condition that the first fluidization region 15 and the second fluidization region 16 are formed in the fluidized bed 14, waste 18 is pushed in one after another by the pusher 41, which makes it possible to suppress intermittent and rapid generation of a combustible gas, thereby stabilizing the gas generation.

In advance of stopping the fluidized bed furnace 10, the pushing of waste 18 into the furnace body 20 by the pusher 41 is firstly stopped. Upon stopping the pushing of waste 18, the gas feeding unit 33 feeds a mixture formed by mixing an inert gas with air, as the fluidizing gas to be supplied to the respective gas boxes 32. In this process, the gas feeding unit 33 operates to gradually increase the inert gas in a ratio between air and the inert gas in the fluidizing gas, with time. In this manner, the gas feeding unit 33 restrains an oxygen concentration within the furnace body 20 to suppress violent or rapid combustion of the waste 18 remaining in the fluidized bed 14.

In this embodiment, during stop of the fluidized bed furnace 10, violent or rapid combustion of the waste 18 remaining in the fluidized bed 14 is suppressed by gradually increasing the ratio of the inert gas occupied in the fluidizing gas. Alternatively, during stop of the fluidized bed furnace 10, combustion of the remaining waste 18 may be prevented by spraying water onto the fluidized bed 14.

As mentioned above, the fluidized bed furnace 10 according to the above embodiment is capable of suppressing intermittent and rapid generation of a combustible gas to stabilize the gas generation, even in a situation where a large amount of easily combustible trash is comprised in waste. Specifically, in the fluidized bed 14, the first fluidization region 15 around the non-combustible substance discharge port 29 and the second fluidization region 16 having a fluidization degree lower than that in the first fluidization region 15 are formed. In this state, new waste 18 is pushed onto the second fluidization region 16. The input of the new waste 18 causes the waste 18 accumulated on the second fluidization region 16 to be moved toward the first fluidization region 15 step-by-step. The above operation will be repeated. Thus, the fluidized bed furnace 10 can sufficiently gasify the waste 18, while suppressing rapid fluctuation of generation of a combustible gas. Consequently, it becomes possible to stably generate a combustible gas from the waste 18. In addition, just after input into the furnace body 20, the waste 18 is not exposed to the highly fluidized bed (the first fluidization region 15), so that it becomes possible to suppress a situation where a large amount of lightweight trash flies up inside the furnace body 20 and undergoes rapid combustion in a free board section.

In the furnace body 20, the upper surface 21 a of the bottom wall 21 is inclined to become lower toward the non-combustible substance discharge port 29. Thus, when non-combustible substances in the waste 18 sinks down to the bottom wall 21 in the fluidized bed 14, they fall on the upper surface 21 a of the bottom wall 21 toward the non-combustible substance discharge port 29. In this manner, the non-combustible substances are discharged from the non-combustible substance discharge port 29 together with a part of the fluidizable particles 12, so that it becomes possible to easily discharge non-combustible substances from the furnace body 20. The non-combustible substances discharged from the non-combustible substance discharge port 29 together with a part of the fluidizable particles 12 are separated from the fluidizable particles 12 in the separation section 52 of the sand circulation device 50.

The furnace body 20 has a shape in plan view, in which a dimension in the width direction thereof is equalized in a pushing direction of waste 18. Thus, when the waste 18 on the second fluidization region 16 is pushed by waste 18 newly pushed by the waste supply section 40, and moved toward the first fluidization region 15, the movement of the waste 18 is stabilized. In addition, a flow of the fluidizable particles 12 formed in a direction from the second fluidization region 16 to the first fluidization region 15 by the sand circulation device 50 is directionally the same as the movement of the waste 18, so that the flow of the fluidizable particles 12 is also stabilized.

In the waste supply section 40, the pusher 41 is adapted to be reciprocatingly moved in a direction parallel to the pushing direction (front-rear direction) to allow the pushing surface 42 to push waste 18 onto the fluidized bed 14 simultaneously by the entire widthwise region of the pushing surface 42. This allows the pushing surface 42 to push waste 18 onto the fluidized bed 14 with an even force in the width direction. Thus, the movement of the waste 18 from the second fluidization region 16 to the first fluidization region 15 is approximately equalized in the width direction, so that it becomes possible to prevent the waste 18 from concentrating on a certain portion inside the furnace.

It is to be understood that a fluidized bed furnace and a waste treatment method of the present invention are not limited to the above embodiment, but various changes and modifications may be made therein without departing from the spirit and scope of the present invention hereinafter defined.

In the above embodiment, the sidewall 22 stands upwardly and straight from the bottom wall 21 to the combustible gas outlet portion 23. Alternatively, for example, as illustrated in FIG. 5, the sidewall may comprise a front wall 24A having a reflecting portion 224 extending toward the rear wall 25 to cover an upper side of the second fluidization region 16 at a predetermined height position. The front wall 24A allows the waste 18 accumulated on the second fluidization region 16 to be heated by radiation heat from the reflecting portion 224. Consequently, it becomes possible to generate a combustible gas from the waste 18 accumulated on the second fluidization region 16. In other words, gasification of the waste 18 accumulated on the second fluidization region 16 is promoted.

Alternatively, as illustrated in FIG. 6, the sidewall may comprise a rear wall 25A having a guide portion 225 extending toward the front wall 24 to cover an upper side of the first fluidization region 15 at a predetermined height position. The guide portion 225 is adapted to guide a high-temperature combustible gas generated from the waste 18 in the first fluidization region 15 to allow the combustible gas to be brought into contact with the waste 18 accumulated on the second fluidization region 16. In this way, the guide portion 225 allows the combustible gas to contribute to heating of the waste 18 accumulated on the second fluidization region 16. Consequently, it becomes possible to promote gasification of the waste 18 accumulated on the second fluidization region 16 without adding special heating means to the furnace body 20.

Alternatively, as illustrated in FIG. 7, the sidewall may comprise a front wall 24B and a rear wall 25B having, respectively, two roof portions 324, 325 extending in a direction causing them to come closer to each other at the same height position. The front wall 24B and the rear wall 25B allow the waste 18 accumulated on the second fluidization region 16 to be heated by radiation heat from the roof portion 324 of the front wall 24B, so as to promote gasification thereof. In addition, a dimension of a furnace body 20B in the front-rear direction is reduced at a position lower than the combustible gas outlet portion 23 at the upper end of the furnace body 20B, so that it becomes possible to facilitate a reduction in size of the furnace body 20B.

In the above embodiment, the upper surface 21 a of the bottom wall 21 has an inclination angle which is constant in the range from the front wall 24 to the non-combustible substance discharge port 29, the present invention is not limited thereto. Alternatively, for example, as illustrated in FIG. 8, an inclination angle α of an upper surface 21 d of a bottom wall 21A on the side of the second fluidization region 16 with respect to a horizontal surface may be greater than an inclination angle β of an upper surface 21 e of the bottom wall 21A on the side of the first fluidization region 15 with respect to the horizontal surface. When the upper surface 21 d supporting the second fluidization region 16 restrained in fluidization, from therebelow, has a relatively large inclination angle in the above manner, non-combustible substances sinking down to the bottom wall 21A more reliably falls to the non-combustible substance discharge port 29. Specifically, the inclination angle β of the upper surface 21 e on the side of the first fluidization region 15 with respect to the horizontal surface is in the range of 15 degrees to 25 degrees, and the inclination angle α of the upper surface 21 d on the side of the second fluidization region 16 with respect to the horizontal surface is in the range of 20 degrees to 75 degrees, preferably, in the range of 20 degrees to 30 degrees.

Alternatively, the upper surface 21 a of the bottom wall 21 may be curved from the front wall 24 to the non-combustible substance discharge port 29, instead of being inclined straight.

As illustrated in FIG. 9, a plurality of thermometers T may be disposed just above the second fluidization region 16, and an air supply section 60 capable of supplying air onto the second fluidization region 16 may be provided. In this fluidized bed furnace, an accumulated amount of the waste 18 accumulated on the second fluidization region 16 can be estimated, so that it becomes possible to control the accumulated amount. Specifically, the accumulated amount of the waste 18 on the second fluidization region 16 is estimated by utilizing a phenomenon that an indication value of the thermometer T embedded in the waste 18 is lowered. When the accumulated amount is relatively large, i.e., the number of the thermometers T embedded in the waste 18 is relatively large, the air supply section 60 is operable to supply air to increase an internal temperature of the furnace body 20. Accordingly, gasification of the waste 18 accumulated on the second fluidization region 16 is prompted, so that the accumulated amount of the waste 18 is reduced. As another method, an amount of the air may be controlled based on determinations made as follows: when a temperature of a designated one of the thermometers T is equal to or greater than a threshold value, it is determined that there is no waste at a position of the designated thermometer T, and, when the temperature is less than the threshold value, it is determined that there is waste at the position of the designated thermometer T (the designated thermometer T is embedded in waste). Alternatively, instead of control of the amount of the air, an amount of waste to be input may be controlled.

In the above embodiment, the gas feeding unit 33 is configured to feed air and/or an inert gas as the fluidizing gas. Alternatively, for example, the gas feeding unit 33 may be configured to feed water vapor and/or oxygen as the fluidizing gas, depending on a combustion state within the furnace body 20. The fluidized bed furnace 10 may further comprise a second gas supply section provided in the sidewall 22 in addition to the first gas supply section 30, wherein the second gas supply section may be configured to be capable of supplying air, oxygen, water vapor or the like into the furnace body 20, depending on a combustion state in the fluidized bed 14 or of the waste 18.

The fluidizing gas to be supplied to the second fluidization region 16 may be a high-temperature fluidizing gas. In the case of supplying the high-temperature fluidizing gas, even in a situation where it is difficult to sufficiently keep a temperature of the second fluidization region 16 only by the circulation of the fluidizable particles 12, the temperature of the second fluidization region 16 can be maintained at a high value without increasing an amount of the fluidizing gas to be supplied.

In the above embodiment, the waste introduction port 28 is provided at a height position partially overlapping with respect to the waste 18 accumulated on the fluidized bed 14 in the up-down direction, so that waste 18 supplied from the waste introduction port 28 positively moves the waste 18 accumulated on the upper surface of the fluidized bed 14, generally horizontally (toward the first fluidization region 15). Alternatively, the fluidized bed furnace 10 may have any configuration capable of supplying waste 18 to a region on the fluidized bed 14 adjacent to the front wall (supply-side sidewall portion) 24. For example, as illustrated in FIG. 10A and FIG. 10B, the waste introduction port 28 may be provided at a height position which is located adjacent to the upper surface of the fluidized bed 14, and free of contact with waste 18 when it is newly supplied onto the waste 18 accumulated (on the second fluidization region 16) in a region of the upper surface of the fluidized bed 14 adjacent to the front wall 24. In this case, as illustrated, for example, in FIG. 10A, the waste introduction port 28 may be provided to allow new waste to be supplied generally horizontally from a height position above the waste 18 accumulated on the fluidized bed 14. Alternatively, as illustrated in FIG. 10B, the waste introduction port 28 may be provided to allow new waste to be supplied downwardly from a height position above the waste 18 accumulated on the fluidized bed 14. Even if waste 18 is supplied into the furnace body 20 in the above manner, when the new waste 18 is supplied onto the accumulated waste 18, a pile of waste 18 is broken and spread, and the spread waste 18 is moved toward the first fluidization region 15. Further, according to the flow of the fluidizable particles 12 formed in the fluidized bed 14 in the direction from the front wall 24 to the non-combustible substance discharge port 29, the waste 18 accumulated on the fluidized bed 14 is also moved toward the first fluidization region 15. Thus, gasification of the waste 18 is sufficiently performed while suppressing rapid fluctuation of generation of a combustible gas to be collected from the fluidized bed furnace 10. Consequently, it becomes possible to stably generate a combustible gas from the waste 18.

In the above embodiment, the fluidizing gas to be supplied to the fluidized bed 14 is supplied in the second fluidization region 16 at a flow velocity satisfying the condition that U_(O)/U_(mf) ranges from 1 to less than 2, and supplied in the first fluidization region 15 at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5, as mentioned above. Alternatively, for example, in a situation where non-combustible substances are accumulated on a furnace floor (the upper surface 21 a of the bottom wall 21) without being discharged to the outside, the fluidizing gas may also be supplied in the second fluidization region 16 at a flow velocity satisfying the condition that U_(o)/U_(mf) ranges from 2 to less than 5, only for a certain period of time in order to discharge the accumulated non-combustible substances to the outside. In this case, preferably, an amount of the fluidizing gas to be supplied to each of the gas boxes 32 is increased step-by-step in a direction from the front wall 24 (left side in FIG. 1) to the rear wall 25 (right side in FIG. 1) of the furnace body 20, instead of blowing the fluidizing gas evenly in the entire second fluidization region 16. Specifically, at a certain time t0, a flow volume of the fluidizing gas to be supplied to the gas box 32 a becomes greater than that of the fluidizing gas to be supplied to each of the remaining gas boxes. Then, at a time t1 after an elapse of several seconds, the flow volume of the fluidizing gas to be supplied to the gas box 32 a is returned to a value during a normal operation, and a flow volume of the fluidizing gas to be supplied to the adjacent gas box 32 b becomes greater than that of the fluidizing gas to be supplied to each of the remaining gas boxes. Then, at a time t2 after a further elapse of several seconds, the flow volume of the fluidizing gas to be supplied to the gas box 32 b is returned to an original value, and a flow volume of the fluidizing gas to be supplied to the adjacent gas box 32 c becomes greater than that of the fluidizing gas to be supplied to each of the remaining gas boxes. Based on the above operation, even if non-combustible substances are accumulated on the furnace floor during the normal operation, it becomes possible to reliably discharge the non-combustible substances to the outside of the furnace body 20. The above specific operation is performed only for a significantly short time, so that an influence on facilities in a subsequent stage can be minimized.

Outline of Embodiment

The outline of the above embodiment is as follows.

The fluidized bed furnace according to the above embodiment is designed to heat waste to extract a combustible gas from the waste. The fluidized bed furnace comprises: fluidizable particles making up a fluidized bed to heat waste; a furnace body having a bottom wall supporting the fluidizable particles from therebelow, and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a non-combustible substance discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance discharge port; a gas supply section for blowing a fluidizing gas from the bottom wall of the furnace body toward the fluidizable particles to fluidize the fluidizable particles; a waste supply section for supplying the waste from a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste on the fluidized bed to be moved toward the non-combustible substance discharge port; and a sand circulation device for returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the waste supply section to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion located on the side opposite to the non-combustible substance discharge port, to the non-combustible substance discharge port, wherein: the gas supply section is adapted to blow the fluidizing gas from around the non-combustible substance discharge port to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern and mixed with the waste to gasify the waste, while blowing the fluidizing gas between the first fluidization region and the waste supply section at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles lower than that in the first fluidization region; and the waste supply section is adapted to supply waste from the supply-side sidewall portion to the fluidized bed to cause the waste to be accumulated on the second fluidization region while causing the accumulated waste to be moved into the first fluidization region step-by-step.

In this fluidized bed furnace, the first fluidization region around the non-combustible substance discharge port and the second fluidization region having a fluidization degree lower than that in the first fluidization region are formed in the fluidized bed. In this state, the waste supply section supplies waste to a region on the fluidized bed adjacent to the supply-side sidewall portion to cause the waste to be accumulated on the second fluidization region while causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step. Thus, gasification of the waste is sufficiently performed while suppressing rapid fluctuation of generation of a combustible gas to be collected from the fluidized bed furnace, so that it becomes possible to stably generate a combustible gas from the waste.

Specifically, fluidization in the second fluidization region is restrained, so that the waste is accumulated on the second fluidization region without being mixed with the fluidizable particles, and easily combustible components of the waste are slowly gasified. Therefore, in the second fluidization region, rapid combustion of the waste is suppressed, and generation of a combustible gas caused by rapid gasification of the waste is minimized. When new waste is supplied into the furnace body by the waste supply section, the waste accumulated on the second fluidization region is moved into the first fluidization region step-by-step. In the first fluidization region, the fluidizable particles are actively fluidized and heated to a high temperature by combustion of the waste, so that the waste moved from a position on the second fluidization region is sufficiently mixed with the fluidizable particles, and thereby the waste is sufficiently gasified to generate a combustible gas. Consequently, it becomes possible to suppress intermittent and rapid generation of a combustible gas, thereby stabilizing the gas generation. A temperature of the second fluidization region is maintained by the sand circulation device which returns the high-temperature fluidizable particles discharged from the non-combustible substance discharge port, to the second fluidization region of the fluidized bed. However, during the period in which the fluidizable particles discharged from the non-combustible substance discharge port are returned to the fluidized bed by the sand circulation device, a temperature of the fluidizable particles is lowered, so that the second fluidization region has a temperature less than that of the first fluidization region.

The upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port, so that, when non-combustible substances in the waste sinks down to the bottom wall in the fluidized bed, they fall on the upper surface of the bottom wall toward the non-combustible substance discharge port. In this manner, the non-combustible substances are discharged from the non-combustible substance discharge port together with a part of the fluidizable particles, so that it becomes possible to easily discharge non-combustible substances from the furnace body.

Preferably, the waste supply section is adapted to push new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step.

According to this feature, new waste is pushed generally horizontally toward the waste accumulated on the second fluidization region. Thus, the waste accumulated on the second fluidization region is pushed by the new waste and reliably moved into the first fluidization region.

Preferably, in the fluidized bed furnace of the present invention, the gas supply section is adapted to blow the fluidizing gas in the second fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2, and blow the fluidizing gas in the first fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles, and U_(o) is a cross-sectional average flow velocity of the fluidizing gas.

The first fluidization region and the second fluidization region can be desirably formed by blowing the fluidizing gas at the above flow velocities. Consequently, it becomes possible to desirably gasify the waste while suppressing rapid combustion of the waste, thereby stably obtaining a combustible gas from the waste.

Preferably, the furnace body has a shape in plan view, in which a dimension in a width direction perpendicular to a pushing direction along which waste is pushed by the waste supply section is equalized in the pushing direction.

According to this feature, when the waste on the second fluidization region is pushed by waste newly pushed by the waste supply section, and moved toward the first fluidization region, the movement of the waste is stabilized, because the dimension of the furnace body in a direction perpendicular to the waste pushing direction (width direction) is equalized. In addition, the flow of the fluidizable particles formed in a direction from the second fluidization region to the first fluidization region by the sand circulation device is directionally the same as the movement of the waste, so that the flow of the fluidizable particles is also stabilized.

Preferably, the waste supply section comprises a pusher having a pushing surface extending in the width direction, and a drive unit for reciprocatingly moving the pusher in a direction parallel to the pushing direction to allow the pushing surface of the pusher to push waste onto the fluidized bed simultaneously by the entire widthwise region of the pushing surface.

According to this feature, waste is pushed onto the fluidized bed with an even force in the width direction, so that the movement of the waste from the second fluidization region to the first fluidization region is approximately equalized in the width direction. Thus, it becomes possible to prevent the waste from concentrating on a certain portion inside the furnace.

The waste treatment method according to the above embodiment is designed to heat waste to extract a combustible gas from the waste. The method comprises: a preparation step of preparing a fluidized bed furnace comprising fluidizable particles making up a fluidized bed to heat the waste, a furnace body having a bottom wall supporting the fluidizable particles from therebelow and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a non-combustible substance discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance discharge port; a fluidization-region formation step of blowing a fluidizing gas from a region of the bottom wall of the furnace body around the non-combustible substance discharge port toward the fluidizable particles to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern, while blowing a fluidizing gas between the first fluidization region and a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles lower than that in the first fluidization region; a fluidizable-particle-flow formation step of returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the supply-side sidewall portion to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion to the non-combustible substance discharge port; and a gasification step of supplying waste from the supply-side sidewall portion to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste to be accumulated on the second fluidization region, while causing the accumulated waste to be moved into the first fluidization region step-by-step and gasified.

In this waste treatment method, the first fluidization region around the non-combustible substance discharge port and the second fluidization region having a fluidization degree lower than that in the first fluidization region are formed in the fluidized bed. Then, the waste is accumulated on the second fluidization region, and the waste accumulated on the second fluidization region is moved into the first fluidization region step-by-step. Thus, gasification of the waste is sufficiently performed while suppressing rapid fluctuation of generation of a combustible gas to be collected from the fluidized bed furnace, so that it becomes possible to stably generate a combustible gas from the waste.

The upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port, so that non-combustible substances in the waste fall on the upper surface of the bottom wall toward the non-combustible substance discharge port. In this manner, the non-combustible substances are discharged from the non-combustible substance discharge port together with a part of the fluidizable particles, so that it becomes possible to easily discharge non-combustible substances from the furnace body.

Preferably, the gasification step includes pushing new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step and gasified.

According to this feature, new waste is pushed generally horizontally toward the waste accumulated on the second fluidization region. Thus, the waste accumulated on the second fluidization region is pushed by the new waste and reliably moved into the first fluidization region, and gasified.

Preferably, in the waste treatment method, the fluidizing gas is blown in the second fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2, and blown in the first fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles, and U_(o) is a cross-sectional average flow velocity of the fluidizing gas.

The first fluidization region and the second fluidization region can be desirably formed by blowing the fluidizing gas at the above flow velocities. Consequently, it becomes possible to desirably gasify the waste while suppressing rapid combustion of the waste, thereby stably obtaining a combustible gas from the waste.

INDUSTRIAL APPLICABILITY

As above, the fluidized bed furnace and the waste treatment method of the present invention are useful in heating waste in a fluidized bed formed by fluidizing fluidizable particles, to extract a combustible gas from the waste, and suitable for stably obtaining a combustible gas even from waste comprising easily combustible trash. 

1. A fluidized bed furnace for heating waste to extract a combustible gas from the waste, comprising: fluidizable particles making up a fluidized bed to heat the waste; a furnace body having a bottom wall supporting the fluidizable particles from therebelow, and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a non-combustible substance discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance discharge port; a gas supply section for blowing a fluidizing gas from the bottom wall of the furnace body toward the fluidizable particles to fluidize the fluidizable particles; a waste supply section for supplying waste from a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste on the fluidized bed to be moved toward the non-combustible substance discharge port; and a sand circulation device for returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the waste supply section to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion located on the side opposite to the non-combustible substance discharge port, to the non-combustible substance discharge port, wherein: the gas supply section is adapted to blow the fluidizing gas from around the non-combustible substance discharge port to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern and mixed with the waste to gasify the waste, while blowing the fluidizing gas between the first fluidization region and the waste supply section at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles lower than that in the first fluidization region; and the waste supply section is adapted to supply waste from the supply-side sidewall portion to the fluidized bed to cause the waste to be accumulated on the second fluidization region while causing the accumulated waste to be moved into the first fluidization region step-by-step.
 2. The fluidized bed furnace as defined in claim 1, wherein the waste supply section is adapted to push new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step.
 3. The fluidized bed furnace as defined in claim 1, wherein the air supply section is adapted to blow the fluidizing gas in the second fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2, and blow the fluidizing gas in the first fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles, and U_(o) is a cross-sectional average flow velocity of the fluidizing gas.
 4. The fluidized bed furnace as defined in claim 1, wherein the furnace body has a shape in plan view, in which a dimension in a width direction perpendicular to a pushing direction along which waste is pushed by the waste supply section is equalized in the pushing direction.
 5. The fluidized bed furnace as defined in claim 4, wherein the waste supply section comprises a pusher having a pushing surface extending in the width direction, and a drive unit for reciprocatingly moving the pusher in a direction parallel to the pushing direction to allow the pushing surface of the pusher to push waste onto the fluidized bed simultaneously by the entire widthwise region of the pushing surface.
 6. A waste treatment method for heating waste to extract a combustible gas from the waste, comprising: a preparation step of preparing a fluidized bed furnace comprising fluidizable particles making up a fluidized bed to heat the waste, a furnace body having a bottom wall supporting the fluidizable particles from therebelow and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a non-combustible substance discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance discharge port; a fluidization-region formation step of blowing a fluidizing gas from a region of the bottom wall of the furnace body around the non-combustible substance discharge port toward the fluidizable particles to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern, while blowing a fluidizing gas between the first fluidization region and a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, at a flow velocity less than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles lower than that in the first fluidization region; a fluidizable-particle-flow formation step of returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the supply-side sidewall portion to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion to the non-combustible substance discharge port; and a gasification step of supplying waste from the supply-side sidewall portion to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste to be accumulated on the second fluidization region, while causing the accumulated waste to be moved into the first fluidization region step-by-step and gasified.
 7. The waste treatment method as defined in claim 6, wherein the gasification step includes pushing new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step and gasified.
 8. The waste treatment method as defined in claim 6, wherein the fluidizing gas is blown in the second fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2, and blown in the first fluidization region at a flow velocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles, and U_(o) is a cross-sectional average flow velocity of the fluidizing gas. 